The present invention relates to a charging generator for a vehicle which does not impose a sudden torque load upon an engine.
A generator is mounted on an automobile to provide power electric loads such as lamps and actuators. In general, this generator makes a field winding rotate by using a part of the torque generated by the engine, generates power by means of a rotating magnetic field generated by the field winding, and maintains the battery voltage at a predetermined value.
When the electric load becomes large, however, control is typically exercised so that the current flowing through the above described field winding suddenly becomes large, and hence an increased proportion of the torque generated by the engine is used for power generation. Therefore, the acceleration performance is degraded or the engine stalls, thereby exerting a bad influence upon the engine.
In order to suppress such a phenomenon, a so-called load response control has been devised, whereby when the electric load becomes large, a sudden increase of a current flowing through the above described field winding is suppressed to prevent an increased proportion of torque generated by the engine from being used for power generation.
In a known load response control as described in JP-A-62-64299, for example, the idle rotation state of an engine is regarded as an increase in proportion of torque used for power generation to the torque generated by the engine and then control is so exercised so as to suppress a sudden increase in current flowing through the field winding.
Further, in a known load response control as described in JP-A-59-83600, for example, lowering of a battery voltage below a predetermined value is regarded as an increase in proportion of torque used for power generation to the torque generated by the engine and then control is exercised so as to suppress a sudden increase in current flowing through the field winding.
Other prior art references are U.S. Pat. No. 4,263,543, U.S. Pat. No. 4,689,545, JP-A-61-203833, JP-A-61-203834 and JP-A-2-184300.
In the former one of the conventional techniques, however, control is always exercised so that the field current may rise only gradually when the engine advances to the idle rotation state. So long as the engine is in the idle rotation state, therefore, rise of the field current is suppressed even if the electric load is not large. Therefore, it becomes impossible to respond to voltage pulsation caused by pulsation of engine rotation and application of a small load. It is thus impossible to keep the battery voltage constant.
That is to say, the former one of the conventional techniques has a problem that when the engine advances to the idle rotation state, the battery voltage cannot be kept constant, resulting in blinking of or troubles in starting of various actuators, for example.
On the other hand, the latter one of the conventional techniques always exercises control so that the field current may rise only gradually when the battery voltage lowers below a predetermined value. In a case other than connection of a large electric load such as the case where the number of engine revolutions is lowered as in deceleration, for example, however, the generator output lowers, resulting in a phenomenon of sudden lowering of the battery voltage. In case the battery voltage lowers, it is necessary to raise the field current as quickly as possible to raise the generator output and thereby raise the battery voltage. Nevertheless, the field current is prevented from rising in this conventional technique. Therefore, the battery voltage cannot be kept at a predetermined value, resulting in a problem of trouble occurrence.